Abstract Details
(2020) Hawaiian Post-Shield Basalts Through Time
Scoates JS, Harrison LN & Weis D
https://doi.org/10.46427/gold2020.2325
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05h: Room 2, Saturday 27th June 06:15 - 06:18
James S. Scoates
View all 3 abstracts at Goldschmidt2020
View abstracts at 2 conferences in series
Lauren N. Harrison View all 3 abstracts at Goldschmidt2020 View abstracts at 4 conferences in series
Dominique Weis View all 12 abstracts at Goldschmidt2020 View abstracts at 22 conferences in series
Lauren N. Harrison View all 3 abstracts at Goldschmidt2020 View abstracts at 4 conferences in series
Dominique Weis View all 12 abstracts at Goldschmidt2020 View abstracts at 22 conferences in series
Listed below are questions that have been submitted by the community that the author will try and cover in their presentation. To submit a question, ensure you are signed in to the website. Authors or session conveners approve questions before they are displayed here.
Submitted by Keith Putirka on Wednesday 24th June 22:39
Hi Lauren - Your isotope data look really interesting. So if I understand correctly, it seems that the plume first nucleated solely within Kea-type mantle, outside of the LLSVP, and sampled only Kea-type manlte ? And then with time, migrated into the LLSVP, but only very recently. Am I seeing that right? If so, what does that mean for the LLSVP as a nominal "hot" region? If not, my apologies. -Keith
Hi Lauren - Your isotope data look really interesting. So if I understand correctly, it seems that the plume first nucleated solely within Kea-type mantle, outside of the LLSVP, and sampled only Kea-type manlte ? And then with time, migrated into the LLSVP, but only very recently. Am I seeing that right? If so, what does that mean for the LLSVP as a nominal "hot" region? If not, my apologies. -Keith
Submitted by Keith Putirka on Thursday 25th June 23:44
Hi Lauren - it seems my first try at posting a question didn't save. I hope this works... It seems like all the very early parts of the plume are Kea-trend composition. Is that right? And that Loa-trend isotopes do not appear until late in the chain? If so, then it seems like the plume nucleated within depleted Kea-trend material, not within the LLSVP; but then the plume migrated into Loa-trend/LLSVP region. If this is correct, then what does this mean about the LLSVP being a hot region that reflects plume nucleation? If I misunderstand, my apologies. -Keith
Hello Keith, yes, all of the early compositions of the Hawaiian mantle plume are Kea like, and this is work done on the Emperor Seamounts by others (Keller et al, 2000; Regelous et al., 2003; Huang et al., 2005; Frey et al., 2005; Shafer et al., 2005). The first Loa trend occurrence is at Daikakuji , a volcano located on the younger, NWHR side of the Hawaiian-Emperor Bend. This is ~47 Ma, so "late in the chain" is a bit relative, although major participation of Loa-type compositions aren't documented until later in the plume towards the younger end of the NWHR after approximately 27 Ma (Harrison and Weis, 2018). You do nail an important issue though--if the edges of the LLSVPs are areas where thermal anomalies are suspected to be elevated above ambient mantle, why wouldn't mantle instabilities that form plumes originate from there, especially when some geodynamic studies have shown that these are likely locations for plume formation? I would simply counter that other geodynamic models have shown that mantle plumes move episodically in the mantle during their lifetimes, and these movements reproduce actual hotspot trails and LIP eruption locations better than fixed plumes (Boschi et al., 2007). We also know that there are multiple areas of anomalous seismic velocity in the deep mantle both inside and outside the LLSVPs that may signify areas of elevated temperature or compositional variations (Yu et al., 2018). Why wouldn't plumes form from one of those areas as well? What we do know about mantle plumes is that they form in a variety of geodynamic conditions that include both the upper and lower mantle, and areas within and without the LLSVP (Montelli et al., 2004; Kumagai et al., 2008; Courtillot et al., 2003). We also have concrete measurements of geochemistry that show that the Emperor Seamount geochemical data does not show mixing relationships that include the Loa enriched end member (EMK of Tanaka et al., 2002), which suggests a complete absence of that component, and thus input of material from the LLSVP, during that time. The movement of the Hawaiian plume, as has been shown by Steinberger et al., 2004; Davaille et al., 2003; Burke and Torsvik, 2004; Hassan et al., 2016, provides a way to explain a lack of LLSVP-enriched material during the formation of the Emperor Seamounts, and the addition of that material later in the lifetime of the Hawaiian plume, and this model is presented in detail in Harrison et al., 2017. Ultimately I don't have the full answer--only geochemical data over the entire Hawaiian-Emperor chain interpreted within the numerous probable conditions suggested as reasonable by geodynamic, plate reconstruction, and deep mantle seismic imaging studies. I think a moving mantle plume explains the geochemical observations well, while still being well supported by geodynamic and seismic results, but who knows what insights further resolution on seismic models and more complexity in geodynamic modelling will bring. To circle back to your question, there's probably more hot regions in the lower mantle outside of the LLSVPs that could form mantle plumes, we just tend to focus on LLSVPs because they are the most obvious and exciting features. -Lauren
Hi Lauren - it seems my first try at posting a question didn't save. I hope this works... It seems like all the very early parts of the plume are Kea-trend composition. Is that right? And that Loa-trend isotopes do not appear until late in the chain? If so, then it seems like the plume nucleated within depleted Kea-trend material, not within the LLSVP; but then the plume migrated into Loa-trend/LLSVP region. If this is correct, then what does this mean about the LLSVP being a hot region that reflects plume nucleation? If I misunderstand, my apologies. -Keith
Hello Keith, yes, all of the early compositions of the Hawaiian mantle plume are Kea like, and this is work done on the Emperor Seamounts by others (Keller et al, 2000; Regelous et al., 2003; Huang et al., 2005; Frey et al., 2005; Shafer et al., 2005). The first Loa trend occurrence is at Daikakuji , a volcano located on the younger, NWHR side of the Hawaiian-Emperor Bend. This is ~47 Ma, so "late in the chain" is a bit relative, although major participation of Loa-type compositions aren't documented until later in the plume towards the younger end of the NWHR after approximately 27 Ma (Harrison and Weis, 2018). You do nail an important issue though--if the edges of the LLSVPs are areas where thermal anomalies are suspected to be elevated above ambient mantle, why wouldn't mantle instabilities that form plumes originate from there, especially when some geodynamic studies have shown that these are likely locations for plume formation? I would simply counter that other geodynamic models have shown that mantle plumes move episodically in the mantle during their lifetimes, and these movements reproduce actual hotspot trails and LIP eruption locations better than fixed plumes (Boschi et al., 2007). We also know that there are multiple areas of anomalous seismic velocity in the deep mantle both inside and outside the LLSVPs that may signify areas of elevated temperature or compositional variations (Yu et al., 2018). Why wouldn't plumes form from one of those areas as well? What we do know about mantle plumes is that they form in a variety of geodynamic conditions that include both the upper and lower mantle, and areas within and without the LLSVP (Montelli et al., 2004; Kumagai et al., 2008; Courtillot et al., 2003). We also have concrete measurements of geochemistry that show that the Emperor Seamount geochemical data does not show mixing relationships that include the Loa enriched end member (EMK of Tanaka et al., 2002), which suggests a complete absence of that component, and thus input of material from the LLSVP, during that time. The movement of the Hawaiian plume, as has been shown by Steinberger et al., 2004; Davaille et al., 2003; Burke and Torsvik, 2004; Hassan et al., 2016, provides a way to explain a lack of LLSVP-enriched material during the formation of the Emperor Seamounts, and the addition of that material later in the lifetime of the Hawaiian plume, and this model is presented in detail in Harrison et al., 2017. Ultimately I don't have the full answer--only geochemical data over the entire Hawaiian-Emperor chain interpreted within the numerous probable conditions suggested as reasonable by geodynamic, plate reconstruction, and deep mantle seismic imaging studies. I think a moving mantle plume explains the geochemical observations well, while still being well supported by geodynamic and seismic results, but who knows what insights further resolution on seismic models and more complexity in geodynamic modelling will bring. To circle back to your question, there's probably more hot regions in the lower mantle outside of the LLSVPs that could form mantle plumes, we just tend to focus on LLSVPs because they are the most obvious and exciting features. -Lauren
Submitted by Dominique Weis on Friday 26th June 19:01
Hi Keith, You understood well - check Harrison et al 2017, Harrison & Weis 2018, publications based on the shield state data. Check also Williamson et al 2019 showing what happens at the beginning of the Hawaiian Islands, i.e. at the level of Kauai. This is where the Loa component is really strengthening. And I am sure that Lauren will pick up with her spin on all this. Thanks, Dominique
Hi Keith, You understood well - check Harrison et al 2017, Harrison & Weis 2018, publications based on the shield state data. Check also Williamson et al 2019 showing what happens at the beginning of the Hawaiian Islands, i.e. at the level of Kauai. This is where the Loa component is really strengthening. And I am sure that Lauren will pick up with her spin on all this. Thanks, Dominique
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